Yes. However, when using a frequency converter to control a wound motor, the rotor winding must be short-circuited, that is, the wound motor is used as a squirrel-cage motor. Because the winding motor is to control the size of the rotor winding series resistance to adjust the speed change. The squirrel cage motor uses a frequency converter to change the stator input (voltage/frequency) of the motor to adjust the speed change.
Frequency modulation technology has three main requirements for motors:
1. Insulation level
2. Forced cooling
3. Rotor bearing
If the speed is adjusted upward beyond the fundamental frequency, the mechanical strength of the motor structure should also be considered.
Generally speaking, the frequency modulation motor is replaced by the ordinary motor, and the frequency modulation transmission is adopted. In principle, yes. From the actual product, it may work or it may not work. i.e. unreliable. Now the motors of foreign brands are no longer divided, and domestic ones are still divided, but some domestic famous brand motor manufacturers have also raised the insulation level of ordinary motors to “F”. The quotation marks mean that this F grade is equivalent to F grade. It is not a real Class F insulation. Its purpose is also for the motor to adapt to the control application of the frequency converter. Therefore, whether ordinary motors can replace variable frequency motors depends on whether the technical conditions of the motor manufacturer meet the requirements of variable frequency control. Instead of saying YES or NO in general.
Ordinary asynchronous motors are designed according to constant frequency and constant voltage, and it is impossible to fully meet the requirements of frequency conversion and speed regulation. The following is the effect of the frequency converter on the motor.
1. The efficiency and temperature rise of the motor.
Regardless of the type of frequency converter, different levels of harmonic voltage and current are generated during operation, so that the motor operates under non-sinusoidal voltage and current. Rejecting the information, taking the commonly used sine wave PWM inverter as an example, its low-order harmonics are basically zero, and the remaining high-order harmonic components that are about twice as large as the carrier frequency are: 2u+1(u is the modulation ratio). Higher harmonics will cause the increase of motor stator copper loss, rotor copper (aluminum) loss, iron loss and additional loss, the most significant is the rotor copper (aluminum) loss. Because the asynchronous motor rotates at a synchronous speed close to the fundamental frequency, the high-order harmonic voltage cuts the rotor bar with a large slip, which will cause a large rotor loss. In addition, additional copper loss due to skin effect needs to be considered. These losses will cause the motor to generate extra heat, reduce the efficiency, and reduce the output power. If the ordinary three-phase asynchronous motor is operated under the condition of non-sinusoidal power output by the frequency converter, its temperature rise will generally increase by 10%-20%.
2. Motor insulation strength problem.
At present, many small and medium-sized inverters use PWM control. Its carrier frequency is about several thousand to more than ten kilohertz, which makes the stator winding of the motor bear a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, so that the inter-turn insulation of the motor can withstand a relatively high voltage. Ordeal. In addition, the rectangular chopper impulse voltage generated by the PWM inverter is superimposed on the motor operating voltage, which will pose a threat to the motor’s ground insulation, and the ground insulation will accelerate aging under repeated high-voltage impacts.
3. Harmonic electromagnetic noise and vibration.
When ordinary asynchronous motors are powered by frequency converters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors will become more complicated. The various time harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces. When the frequency of the electromagnetic force wave is the same as or close to the natural vibration frequency of the motor body, a resonance phenomenon will occur, thereby increasing the noise. Due to the wide operating frequency range of the motor and the large range of speed variation, it is difficult for the frequency of various electromagnetic force waves to avoid the natural vibration frequency of each component of the motor.
4. The adaptability of the motor to frequent starting and braking.
After the inverter is used for power supply, the motor can be started at a very low frequency and voltage without inrush current, and various braking methods provided by the inverter can be used for rapid braking. In order to achieve frequent starting and braking Conditions are created, so the mechanical system and electromagnetic system of the motor are under the action of cyclic alternating force, which brings fatigue and accelerated aging problems to the mechanical structure and insulation structure.
5. Cooling problem at low speed.
First of all, the impedance of the asynchronous motor is not ideal. When the power frequency is low, the loss caused by high-order harmonics in the power supply is relatively large. Secondly, when the speed of ordinary asynchronous motors decreases, the cooling air volume decreases proportionally to the cube of the speed, resulting in the deterioration of the cooling condition of the motor at low speeds, a sharp increase in temperature rise, and it is difficult to achieve constant torque output.
Yes. However, when using a frequency converter to control a wound motor, the rotor winding must be short-circuited, that is, the wound motor is used as a squirrel-cage motor. Because the winding motor is to control the size of the rotor winding series resistance to adjust the speed change. The squirrel cage motor uses a frequency converter to change the stator input (voltage/frequency) of the motor to adjust the speed change.
Frequency modulation technology has three main requirements for motors:
1. Insulation level
2. Forced cooling
3. Rotor bearing
If the speed is adjusted upward beyond the fundamental frequency, the mechanical strength of the motor structure should also be considered.
Generally speaking, the frequency modulation motor is replaced by the ordinary motor, and the frequency modulation transmission is adopted. In principle, yes. From the actual product, it may work or it may not work. i.e. unreliable. Now the motors of foreign brands are no longer divided, and domestic ones are still divided, but some domestic famous brand motor manufacturers have also raised the insulation level of ordinary motors to “F”. The quotation marks mean that this F grade is equivalent to F grade. It is not a real Class F insulation. Its purpose is also for the motor to adapt to the control application of the frequency converter. Therefore, whether ordinary motors can replace variable frequency motors depends on whether the technical conditions of the motor manufacturer meet the requirements of variable frequency control. Instead of saying YES or NO in general.
Ordinary asynchronous motors are designed according to constant frequency and constant voltage, and it is impossible to fully meet the requirements of frequency conversion and speed regulation. The following is the effect of the frequency converter on the motor.
1. The efficiency and temperature rise of the motor.
Regardless of the type of frequency converter, different levels of harmonic voltage and current are generated during operation, so that the motor operates under non-sinusoidal voltage and current. Rejecting the information, taking the commonly used sine wave PWM inverter as an example, its low-order harmonics are basically zero, and the remaining high-order harmonic components that are about twice as large as the carrier frequency are: 2u+1(u is the modulation ratio). Higher harmonics will cause the increase of motor stator copper loss, rotor copper (aluminum) loss, iron loss and additional loss, the most significant is the rotor copper (aluminum) loss. Because the asynchronous motor rotates at a synchronous speed close to the fundamental frequency, the high-order harmonic voltage cuts the rotor bar with a large slip, which will cause a large rotor loss. In addition, additional copper loss due to skin effect needs to be considered. These losses will cause the motor to generate extra heat, reduce the efficiency, and reduce the output power. If the ordinary three-phase asynchronous motor is operated under the condition of non-sinusoidal power output by the frequency converter, its temperature rise will generally increase by 10%-20%.
2. Motor insulation strength problem.
At present, many small and medium-sized inverters use PWM control. Its carrier frequency is about several thousand to more than ten kilohertz, which makes the stator winding of the motor bear a high voltage rise rate, which is equivalent to applying a steep impulse voltage to the motor, so that the inter-turn insulation of the motor can withstand a relatively high voltage. Ordeal. In addition, the rectangular chopper impulse voltage generated by the PWM inverter is superimposed on the motor operating voltage, which will pose a threat to the motor’s ground insulation, and the ground insulation will accelerate aging under repeated high-voltage impacts.
3. Harmonic electromagnetic noise and vibration.
When ordinary asynchronous motors are powered by frequency converters, the vibration and noise caused by electromagnetic, mechanical, ventilation and other factors will become more complicated. The various time harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces. When the frequency of the electromagnetic force wave is the same as or close to the natural vibration frequency of the motor body, a resonance phenomenon will occur, thereby increasing the noise. Due to the wide operating frequency range of the motor and the large range of speed variation, it is difficult for the frequency of various electromagnetic force waves to avoid the natural vibration frequency of each component of the motor.
4. The adaptability of the motor to frequent starting and braking.
After the inverter is used for power supply, the motor can be started at a very low frequency and voltage without inrush current, and various braking methods provided by the inverter can be used for rapid braking. In order to achieve frequent starting and braking Conditions are created, so the mechanical system and electromagnetic system of the motor are under the action of cyclic alternating force, which brings fatigue and accelerated aging problems to the mechanical structure and insulation structure.
5. Cooling problem at low speed.
First of all, the impedance of the asynchronous motor is not ideal. When the power frequency is low, the loss caused by high-order harmonics in the power supply is relatively large. Secondly, when the speed of ordinary asynchronous motors decreases, the cooling air volume decreases proportionally to the cube of the speed, resulting in the deterioration of the cooling condition of the motor at low speeds, a sharp increase in temperature rise, and it is difficult to achieve constant torque output.
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